1. Field of the Invention
This invention relates to a copper-based alloy which permits elimination or reduction of defilement with lead and excels in tolerance for dezincification, hot forgeability, or machinability, a method for the production of this alloy, and products using this alloy.
2. Description of the Prior Art
Generally in the copper-based alloys of this class, Cu—Zn brass alloys and Cu—Sn bronze alloys each having Cu as a main component are being used extensively.
Particularly, the brass alloys have been finding extensive dissemination because they are excellent in corrosion resistance, workability, forgeability, and mechanical properties and are also favorable in terms of price as compared with other copper-based alloys.
The brass alloys are known in various types, such as free cutting brass (C3604 of JIS [Japanese Industrial Standard] H3250), forging grade brass (JIS C3771) and brass (BS [British Standard] CZ132).
Particularly, the free cutting brass bar has a high Pb content of 1.8-3.7%. When it is used in a metallic part, such as the valve that by nature operates in water, it encounters difficulty in satisfying the condition of the standard tolerance for Pb liquation (not more than 0.05 mg/liter, for example) because it liquates the Pb out into the water. The problem posed by such lead liquation, therefore, needs a prompt solution.
The free cutting brass bar is a brass material which has the α+β phase for the texture thereof and, in relative ratios, contains Cu predominantly in the α phase and Zn likewise in the β phase. When this brass bar is retained in the atmosphere of a corrosive liquid, therefore, it forms a local cell from the potential difference between the α phase and the β phase and induces liquation of Zn and corrosion by dezincification.
Then, the ordinary forging grade brass bar combines the problem of liquation of Pb and the problem of corrosion by dezincification similarly to the free cutting brass bar.
As a measure against the problem of environment pollution due to this liquation of lead, the technique of producing blue brass incorporating Bi singly or Se and Bi jointly into a copper-based alloy in place of Pb with a view to eliminating the influence of the lead has been already suggested (U.S. Pat. No. 5,614,038).
Further, the technique of perfecting bronze by adding P to the technique for combating the lead as described above thereby forming an intermetallic compound, Cu3P, and enhancing the wear resistance thereof has been known (JP-A-08-120369). Various other techniques for combating lead have been suggested.
The conventional copper-based alloy materials have originated in the lead-combating technique that is directed at copper-based alloys. No technique that additionally excels in tolerance for dezincifiction as well as in machinability and forgeability has yet been known. No copper-based alloy that has solved a further particular problem of the tolerance for corrosion by dezincification peculiar to brass has yet been developed. Such is the true state of the conventional copper-based alloys.
This invention has been perfected as a result of a diligent study pursued with a view to solving the problems of the prior art. It is directed at clearing the problem of environmental pollution by the liquation of lead and, at the same time, providing a copper-based alloy of brass or bronze excelling in tolerance for dezincification, machinability, and hot forgeability.